1. Field of the Invention
The present invention relates to an improved blowing agent composition, comprised of (i) azodicarbonamide: (ii) at least one member selected from the group consisting of zinc oxide and zinc carbonate; and (iii) at least one member selected from the group consisting of the zinc salts of C.sub.1 -C.sub.6 organic acids and C.sub.1 -C.sub.6 carboxamides. In other aspects, this invention relates to the preparation and use of such blowing agents, as well as to foamable polymeric compositions comprising foamable polymers and such blowing agent compositions.
2. Description of Related Art
In the manufacture of expanded polymeric materials (such as polyurethanes, polyolefins and the like) the polymeric material is conventionally mixed with a blowing agent which, upon exposure to elevated temperature conditions, decomposes to form gaseous decomposition products for expansion of the material.
Among conventionally employed blowing agents, azodicarbonamide has come into widespread usage, largely due to its broad applicability in plastics and elastomers. Moreover, this blowing agent is non-toxic, odorless and non-flammable in character, and its decomposition products present no dangerous health hazards. However, azodicarbonamide has the disadvantage that its decomposition temperature is relatively high, 210.degree. C., rendering it difficult to utilize with many polymeric materials--particularly those having low softening temperatures or which are otherwise susceptible to thermal degradation or deterioration. Consequently, when used with polymeric materials having such disadvantageous thermal characteristics, it is desirable to add a decomposition accelerator (activator) to lower the decomposition temperature of the azodicarbonamide blowing agent.
Among the activators useful for reducing the decomposition temperature of azodicarbonamide are lead, zinc, tin and cadmium oxides, urea and various amines. While the use of such activators reduces the otherwise undesirably high decomposition temperature of azodicarbonamide, such activator-containing blowing agent compositions have the disadvantage that the rate and level of gas evolution at lower temperatures is undesirably low. Specifically, the amounts and rate of gas formed on decomposition of azodicarbonamide under low temperature activated conditions are less than those amounts obtained from decomposition of such compound at its normal high decomposition temperature.
As a result of the foregoing disadvantages, azodicarbonamide has been somewhat limited in the low temperature commercial manufacture of foamed (expanded) products.
It therefore would be highly desirable to provide azodicarbonamide in a blowing agent composition wherein the decomposition temperature for such compound is reduced and wherein the adverse impact on the volume of gas and gas evolution rates obtained therefrom is reduced or eliminated.
U.S. Pat. No. 4,312,776 to Puri et al discloses a blowing agent composition comprising azodicarbonamide, a chromium sulfate and at least one zinc compound selected from zinc salts and oxides.
A blowing agent composition comprising (a) azodicarbonamide, (b) zinc oxide, zinc carbon or a zinc salt of C.sub.1 -C.sub.4 organic acid, and (c) an aromatic sulfinic acid or a metal salt of an aromatic sulfinic acid is disclosed in U.S. Pat. No. 4,444,679 to Rowland et al.
Japanese Patent Application No. 53145876-A describes a foamable vinyl chloride resin composition utilizing as a foaming assistant at least one zinc salt of C.sub.1 -C.sub.6 organic carboxylic acid and azodicarbonamide. Specific carboxylic acids disclosed in this application include formic, acetic, caproic, tartaric and glycolic acids. The zinc salt is employed at a concentration of 0.5-2 weight percent based on the weight of the resin, which in addition to vinyl chloride polymers may also include other polymers such as synthetic rubbers.
A process for the production of a cellular polychloroprene vulcanizate using azodicarbonamide and at least one metal oxide as a blowing agent is disclosed in U.S. Pat. No. 3,846,350.
Japanese Patent Publication No. 133433 discloses a blowing agent composition of azodicarbonamide and the reaction product of an amine with a zinc compound.
Zinc formate compositions are described in British Pat. No. 1,567,417 (use of zinc formate in foamable polyester compositions to impart improved flame retardant properties); U.S. Pat. No. 4,438,223 ( a blowing agent composition comprising zinc formate and certain inorganic and organic alkali metal activators); Dollimore et al, Journal Of Inorganic Nuclear Chemistry, 29, 621-627 (1967) (disclosing the decomposition behavior of zinc and manganous formates); and Djega-Mariabassou et al, Bull. Soc Chim. France, 9, 3166-3173 (1971), "Study of Decompositions Causing Simultaneous Release of Several Gases, IV--Thermal Decomposition Of Zinc Formate Dihydrate and Morphology of Zinc Oxide Residual" (describing the decomposition behavior of zinc formate and the role of zinc oxide formed during its decomposition). German Offenlegungsschrift No. 2,148,099 described the expansion of thermoplastic polymers using neutral metal salts of formic and/or oxalic acid optionally with a stabilizer such as sodium phosphite.
U.S. Pat. No. 4,554,294 discloses the use of zinc salts of nitro urea in blowing agent compositions.